Hi,
On 3-5-2011 22:38, Angela Kemmler wrote:
In Europe you may find quite often a power outlet (wall outlet) without "earth" contact,
so, this contact is not necessary. You find extension cords with only two wires. The third
("earth") contact has only the purpose to protect you. In Germany you find often a
particular fuse interrupting the tension, if a current above 10 mA flows over the earth contact.
I'm sure this is also the case in other countries.
To be more precise, the third (Yellow-green wire) is there to let a
potential "leaking-current" from the equipment or housing flow back to
the grid.
Be aware that the current flowing through this earth-wire can be lethal !
However in Europe in most houses in the meter cupboard (where the 230
VAC is distributed through the house) always a maximum of 4 combined
groups (usually 16 A each) are protected by a single electro-mechanical
30 mA differential circuit-breaker, which is activated (via a solenoid)
when the current-difference between the Live (Brown wire) and Neutral
(Blue wire) pair exceeds the 30 mA.
Where this leaking-current is flowing is not relevant for this
circuit-breaker, it may well be over a copper gas-pipe or water-pipe and
not always necessarily over a dedicated earth-conductor as long as it is
below the threshold, it will not activate the circuit-breaker.
Kind regards,
MoB
